why not? you can record anything you can get out of a modulator or component cables.
receiver still does tuning but picture and sound can come from iMac just like PC
if iMac can record video/audio in then it can record.
no need for new receiver. 622 will work just fine. it has the outputs to do the job just fine. if I read the specs right you will need the Elegato EyeTV HD either way.